QJEEM19Chf945: JEE Main 2019 Chemistry - Class 11 JEEM19Chf945 Solution: The hardness of a water sample (in terms of equivalents of CaCO …

Question

Verified Solution • 2025–26 Session moderate

The hardness of a water sample (in terms of equivalents of CaCO₃) containing 10^–3 M CaSO₄ is (Molar mass of CaSO₄ = 136 g mol^–1)

Accepted Answer

n_CaSO₄

\times

Van't hoff factor = n_CaCO₃

\times

Van't hoff factor

\Rightarrow

10^-3

\times

2 = n_CaCO₃

\times

2

\Rightarrow

n_CaCO₃ = 10^-3 mol in 1 L

∴

w_CaCO₃ = 100

\times

10^-3 g CaCO₃ in 1 L solution

∴

hardness in terms of CaCO₃

=

\frac{w_{C a C O_{3}}}{w_{T o t a l}} \times 10^{6}

=

\frac{100 \times 10^{- 3}}{1000} \times 10^{6}

= 100 ppm

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